Endocrinological manipulations and initial maternal behaviour in the Virgin rat (Rattus norvegicus)

Abstract

Steroidal hormones are known to mediate maternal behaviour by influencing specific neural structures that are responsible for initial onset and maintenance of this behaviour. Contrary to typical extirpation and replacement strategies, this study examined hormonally intact animals to evaluate the specific effects of hormonal enhancement in conjunction with endogenous fluctuations on maternal behaviour. Rats were given a regimen of estrogen and progesterone hormones via osmotic pumps and subcutaneous injections to mimic natural pregnancies. Maternal behaviours were recorded for a twenty-four hour observation period either immediately after parturition or after a sensitization period to foster pups. Neural tissue was removed from the medial preoptic area after the observation period and prepared for future analysis with electron microscopy. Behavioural results from this study revealed that initial behaviours are not influenced in exogenously enhanced virgins compared to virgin and pregnant controls. These results suggest the significance of neural moderation on the onset and magnitude of maternal behaviour.